Networked polymeric gels and use of such polymeric gels in hydrocarbon recovery

ABSTRACT

A composition includes water having a salinity of at least 1 ppt, at least one hydrophilic polymer containing primary (—NH 2 ) and/or secondary (—NHR) amine groups and at least one saccharide containing a reducible function. A method of changing the permeability of a subterranean formation includes the step of injecting into a subterranean formation a composition comprising water, at least one hydrophilic polymer containing at least two groups which are independently the same or different a primary amine group or a secondary amine group and at least one saccharide containing a reducible function.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims the benefit of U.S. Provisional PatentApplication Ser. No. 60/548,300, filed Feb. 27, 2004, the disclosures ofwhich are incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to crosslinked or networked polymeric gelsand to methods of hydrocarbon production or recovery from undergroundformations using such networked polymeric gels, and, especially, tonetworked polymeric gels that are suitable to withstand hightemperatures and/or high salt content/salinity (for example, commonlyexperienced in hydrocarbon/oil production and recovery) and to methodsof using such gels in hydrocarbon/oil production or recovery.

Gelled or crosslinked water-soluble polymers have been widely used inenhanced oil recovery operations. For example, such gelled polymers canbe used to alter the permeability of underground formations to enhancethe effectiveness of water flooding operations. In a number ofapplication, polymers and appropriate crosslinking agents or systems areinjected in an aqueous solution into the underground formation.Preferably, the polymers permeate into regions having the highest waterpermeability and gel therein. Fluids injected into the formation insubsequent water flooding operations, are, for example, diverted awayfrom the regions in which the gel formed to areas containing unrecoveredoil.

It is generally desirable that polymers used in processes for therecovery of oil and other hydrocarbons impart to a liquid an increasedviscosity when a relatively small quantity of the polymer is added. Theincreased viscosity is preferably achieved at a minimal cost. It is alsodesirable that such polymers form gels, for example, in the presence ofa gelling agent such as a crosslinking agent, in the desired undergroundformations and do not gel before they can effectively penetrate thedesired underground formations. Many processes have been developed todelay the gelation of gelling compositions by adding a delaying agent.However, such gelation delaying agents often add significant costs tooil field operation.

Although many polymers have been developed and used in hydrocarbon/oilrecovery processes, many of these polymers cannot adequately withstandthe hostile environments present in oil recovery. For example, many suchpolymer are incapable of forming gels having sufficient thermalstability, particularly in harsh environments such as in watercontaining high salinity.

Many polymer systems currently used in the oil recovery systems alsoinclude environmentally undesirable components. For example, in certainsystems chromium crosslinking agents are used to produce gels ofincreased stability. However, a chromium salt is not an environmentallydesirable compound and increased costs may be incurred to preventcontamination of ground water sources. Likewise, many conventionalcrosslinking systems include environmentally undesirable phenoliccompound (known to be toxic) and/or formaldehyde (known to be acarcinogen).

It is desirable to develop water-soluble polymers that can be used toprepare crosslinked polymer networks/gels that withstand hostileenvironments such as those found in hydrocarbon/oil recovery.

SUMMARY OF THE INVENTION

In one aspect, the present invention provides a composition comprisingwater having a saline content of at least 1 ppt (part per thousand), atleast one hydrophilic polymer containing primary (—NH₂) and/or secondary(—NHR) amine groups (that is, the hydrophilic polymer contains orincludes at least two groups which are independently the same ordifferent a primary amine group or a secondary amine group) and at leastone saccharide containing a reducible function. In general, the Rsubstituent upon the secondary amine is not limited. Strong electronwithdrawing groups are not preferred as such groups can reduce thenucleophilic nature of the secondary amine. In many cases, R is an alkylgroup. The amine groups can be pendant groups on the polymer orincorporated into the polymer backbone. In general, the hydrophilicpolymer must include at least two amine groups (per a polymer chain) toenable crosslinking.

The surprising stability of networked polymeric gels of the presentinvention in waters having high salt content/salinity makes thenetworked polymeric gels useful for injection into subterranean orunderground formations to alter the permeability thereof in, forexample, the recovery of oil and/or other hydrocarbons. Moreover,because of environmental concerns as well as cost for disposing of aproduced brine (that is, water of relatively high salinity co-producedwith oil and gas, which is generally contaminated with some oil, or gas,or both) it may be desirable to utilize produced brine as theliquid/water used for the networked polymeric gels of the presentinvention. Use of produced brines eliminates the cost associated withacquiring fresh water for use as the liquid and the disposal cost forthe produced brine. Although the networked polymeric compositions of thepresent invention may be particularly suited for use in hydrocarbonrecovery, the networked polymeric compositions of the present inventioncan be used in virtually any device, system or method in which it isdesirable to form a crosslinked polymer network in water of relativelyhigh salinity.

The term “salinity” has been defined in a number of manners over thelast century. At the simplest level, the term “salinity” refersgenerally to the total amount of dissolve solids (in grams) in 1000grams (1 kg) of water, and is described as parts per thousand (ppt). Theeleven ions that comprise the majority of the solids in seawater are (ingrams per kilogram of water): Chloride (19.135), Sodium (10.76), Sulfate(2.712), Magnesium (1.294), Calcium (0.413), Potassium (0.387),Bicarbonate (0.142), Bromide (0.067), Strontium (0.008), Boron (0.004),and Fluoride (0.001). See, Turekian, Karl. Oceans, Englewood Cliffs,N.J.: Prentice-Hall Inc, 1976. However, for a number of reasons it isalmost impossible to measure the total dissolved materials in practice(for example, volatile materials such as gases cannot be accuratelymeasured and chlorides are lost in drying). In an effort to avoid suchproblems, the definition of salinity was revised in 1902 to refer to thetotal amount of solid materials in grams dissolved in one kilogram ofwater when all carbonate has been converted to oxide, the bromine andiodine replaced by chlorine and all organic matter completely oxidized.

The above definition is still difficult to implement in practice. In1966, the Joint Panel on Oceanographic Tables and Standards (appointedby UNSECO and other international organizations) recommended thatsalinity and chlorinity be related using the formula:

S=1.80655 Cl

wherein chlorinity Cl is defined as the mass of silver required toprecipitate completely the halogens in 0.3285234 kg of a water sample.More recently, conductivity meters have been used to measure salinity.The Practical Salinity Scale of 1978 is currently the officialdefinition of salinity:

S _(psu)=0.0080−0.1692R ^(1/2) ₁₅+25.3851R _(T)+14.0941R ^(3/2)_(T)−7.0261R ² _(T)+2.7081R ^(5/2) _(T) +ΔS

R _(T) =C(S,T,0)/C(KCl,T,0)

ΔS=[(T−15)/(1+0.0162(T−15))]+0.005−0.0056R ^(1/2) _(T)−0.0066R_(T)−0.0375R ^(3/2) _(T)+0.636R ² _(T)−0.0144R ^(5/2) _(T)

2≦S≦42

wherein C(S, T, 0) is the conductivity of the sea-water sample attemperature T and standard atmospheric pressure, and C (KCl, T, 0) isthe conductivity of the standard potassium chloride (KCl) solution attemperature T and standard atmospheric pressure. The standard KClsolution contains a mass of 32.435 6 grams of KCl in a mass of 1.000000kg of solution. An extension of the above equation gives salinity at anypressure. Stewart, R. H, Introduction to Physical Oceanography,Department of Oceanography, Texas A & M University, Chapter 6 (August2003 edition), which is available on the Internet at the following URL:http://oceanworld.tamu.edu/resources/ocng_textbook/PDF_files/book.pdf.Salinity determined from the Practical Salinity Scale is abbreviatedpsu, for practical salinity units.

Fresh water typically has a salinity of well less that 1 ppt (or 1000parts per million, ppm). Indeed, the salinity of fresh water varieswidely, but is typically less than 0.5 ppt. On the other hand, seawatertypically has a salinity in the range of approximately 20 to 40 ppt,with an average salinity of approximately 35 ppt. While still forming astable crosslinked network, the compositions of the present inventioncan incorporate water having a salinity (as measured using The PracticalSalinity Scale of 1978) of at least any value in the range ofapproximately 0.5 to 3 ppt. Further, the compositions of the presentinvention can incorporate water having a saline content of at least 10ppt. Still further, the compositions of the present invention canincorporate water having a saline content of at least 20 ppt. Indeed,the compositions of the present invention can incorporate water having asaline content of at least 35 ppt.

Moreover, unlike many networking polymeric systems currently use inhydrocarbon recovery, the networked polymeric gels of the presentinvention are inherently thermally stable at the temperatures (often inexcess of 90° C. or even 110° C.) found in subterranean formations fromwhich such materials are recovered. Indeed, gelation of the networkedpolymeric gels of the present invention occurs best at temperaturesabove 80° C. The temperature dependence of the compositions of thepresent invention can also assist in preventing gelation prior to or tooearly during injection, thereby reducing or eliminating the necessity ofdelaying agents and the costs and other problems associated therewith.

The amine functional polymer/reducible saccharide combinations of thepresent invention have been found to undergo an unexpected cross-linkingreaction in water of high salt content upon the application of heat. Thepolymers used in the compositions of the present invention can behomopolymers and/or copolymers (which are polymerized from two or moredissimilar monomers). As used herein, the term “polymer” refersgenerally to a compound having multiple repeat units (or monomer units)and includes the term “oligomer,” which is a polymer that has only a fewrepeat units. The term “copolymer” refers to a polymer including two ormore dissimilar repeat units (including terpolymers—comprising threedissimilar repeat units—etc.).

Polymers suitable for use in the present invention include, but are notlimited to, partially hydrolyzed poly(N-vinylformamide) (that is, acopolymer of NVF and vinylamine), partially hydrolyzed vinyl acetate/NVFcopolymer (that is, a polymer with vinyl acetate, vinyl alcohol, NVF andvinylamine repeat units); hydrolyzed acrylonitrile/NVF copolymer;(available as a commercial product from Mitsubishi and containingacrylonitrile, acrylamide, amidine, NVF and vinylamine units), aminefunctional polyacrylamide (for example, prepared via Hoffman degradationof polyacrylamide), acrylic acid/vinylamine copolymer, maleicanhydride/maleic acid copolymers with NVF/vinylamine, NVF/vinylaminepolymers with vinyl sulfonate comonomer units, allylamine/diallylaminepolymers and copolymers, urea/formaldehyde and melamine/formaldehydecondensation polymers, amidoamine polymers (prepared from dicarboxylicacids and polyfunctional amines), amine/epichlorohydrin polymers,poly(ethyleneimine), hydrolyzed or partially hydrolyzedpoly(2-alkyl-2-oxazoline) poly(diallyl dimethyl ammonium chloride),diallyl dimethyl ammonium chloride/acrylamide copolymer, diallyldimethyl ammonium chloride/diallyl amine copolymer, and diallyl dimethylammonium chloride/allyl amine copolymer. One hydrophilic polymer or amixture of two or more such polymers can be used in compositions of thepresent invention.

In one embodiment, the hydrophilic polymer is at least one ofpoly(diallyl dimethyl ammonium chloride), diallyl dimethyl ammoniumchloride/acrylamide copolymer, diallyl dimethyl ammoniumchloride/diallyl amine copolymer, or diallyl dimethyl ammoniumchloride/allyl amine copolymer. In the case that the hydrophilic polymeris diallyl dimethyl ammonium chloride/acrylamide copolymer, diallyldimethyl ammonium chloride/diallyl amine copolymer, or diallyl dimethylammonium chloride/allyl amine copolymer, the content of diallyl dimethylammonium chloride in the copolymer can be at least 50 weight percent. Arelatively high concentration of diallyl dimethyl ammonium chloridegenerally increases water solubility. The content of diallyl dimethylammonium chloride in the copolymer can also be at least 70 weightpercent. Moreover, the content of diallyl dimethyl ammonium chloride inthe copolymer can further be at least 80 weight percent. Of the abovediallyl dimethyl ammonium chloride copolymers, preferred copolymer arediallyl dimethyl ammonium chloride/diallyl amine copolymer and diallyldimethyl ammonium chloride/allyl amine copolymer.

As clear to one skilled in the art, the hydrophilic polymers of thepresent invention are readily synthesized as homopolymers or copolymers(including terpolymers etc.) prepared from, for example, mono- ordi-unsaturated (that is, including one or two carbon-carbon doublebonds) primary and secondary amines or amine monomers. Copolymerizationcan occur with, for example, unsaturated amides, carboxylic acids,anhydrides, sulfonic acids, hydrolyzed amides, and/or condensationpolymers. Depending upon the chemical structure of the hydrophilicpolymer(s) used in the compositions, the compositions of the presentinvention can form a covalently crosslinked polymer network or anionically crosslinked polymer network.

In general, polymers having a broad range of number average molecularweight (Mw) are suitable for use in the present invention. Preferably,the molecular weight of the polymers is at least approximately 500. Morepreferably, the molecular weight is in the range of approximately 30,000to approximately 1,000,000. Polymers having molecular weight in excessof 100,000 can be used, but water solubility of certain polymerstypically decreases for such polymers as molecular weight increasesbeyond approximately 100,000.

The reducible saccharides used in the present invention can bemonosaccharides, disaccharides, trisaccharides etc, (for example,sugars) or polysaccharides (for example, starch or cellulose).Polysaccharides are typically a combination of nine or moremonosaccharides. Reducible saccharides or reducing saccharides include areducing group, function or functionality which is typically an aldehydegroup (—C(O)H) or a hemiacetal group

which is another form of an aldehyde when the saccharide is in a cyclicconformation. Examples of reducing saccharides suitable for use in thepresent invention include, but are not limited to, the sugars glucose,lactose, and 2-deoxy-D-ribose. To decrease costs, the saccharide ispreferably a monosaccharide (for example, glucose), a disaccharide (forexample, lactose) or a polysaccharide (for example, starch).

The composition can, for example, further include a base. Examples ofsuitable bases include, but are not limited to, sodium hydroxide,potassium hydroxide, ammonia or calcium carbonate.

In one embodiment, the polymer is a copolymer of vinyl amine and vinylalcohol. Preferably, the copolymer is at least 0.5% by weight of vinylamine. More preferably, the copolymer is at least 3% by weight of vinylamine. Even more preferably, the copolymer is at least 6% by weight ofvinyl amine. Copolymers having well in excess of 6% by weight of vinylamine are suitable for use in the present invention. In severalembodiments for example, copolymer can be at least 12% by weight ofvinyl amine.

A broad range of mole ratios of amine to reducing saccharide is suitablefor use in the present invention. In one embodiment, the mole ratio ofamine groups to reducing saccharide is in the range of approximately 1:4to approximately 8:1. Preferably, the mole ratio of amine groups toreducing saccharide is in the range of approximately 1:2 toapproximately 8:1. In general, increasing amine content results instiffening of the resultant gel. One skilled in the art can readilydetermine an appropriate amine content for a desired set of propertiesfor the resultant gel.

In another aspect, the present invention provides a method of changingthe permeability of a subterranean formation including the step ofinjecting into a subterranean formation a composition comprising water,at least one hydrophilic polymer containing at least two groups whichare independently the same or different a primary amine group or asecondary amine group and at least one saccharide containing a reduciblefunction. The water can be “fresh” water (that is water, typicallyhaving a salinity of less than 0.5 ppt) or can be water of relativelyhigh salinity (that is, greater than 0.5 ppt) as discussed above. In oneembodiment, the composition is formed at a temperature belowapproximately 50° C., or more typically, at room temperature or below(that is, at approximately 25° C. or below) and subsequently heatedin/by the environment of the subterranean formation to inducecross-linking.

In still a further aspect, the present invention provides a method of afluid (for example, a hydrocarbon such as oil) from a subterraneanformation including the step of injecting into a subterranean formationa composition comprising water, at least one hydrophilic polymercontaining at least two groups which are independently the same ordifferent a primary amine group or a secondary amine group and at leastone saccharide containing a reducible function.

The compositions of the present invention can be injected as individualcomponents or as a pre-gel made by the partial reaction of thepolymer(s) or copolymer(s) and the reducible saccharide component(s). Notoxic crosslinking agents, oxidizing agents, phenolic compounds,formaldehyde or organohalo compounds are required in the compositionsand methods of the present invention. In general, no environmentallyundesirable components are used in the compositions and methods of thepresent invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a study of gel time at various temperatures for acomposition including a copolymer of vinyl amine and vinyl alcohol (6 wt% vinyl amine) and D-glucose at a 1:1 sugar/copolymer ratio.

FIG. 2 illustrates the effect of addition of base upon gel time.

FIG. 3 illustrates a study of gel time at various sugar:copolymer ratiosfor a composition including a copolymer of vinyl amine and vinyl alcoholand D-glucose.

FIG. 4 illustrates a study of gel time at various sugar:copolymer ratiosfor a composition including a copolymer of vinyl amine and vinyl alcoholand lactose.

FIG. 5 illustrates the viscosity of a composition including a copolymerof vinyl amine and vinyl alcohol (6 wt % vinyl amine) and D-glucose at a1:1 sugar/copolymer ratio as a function of time.

FIG. 6 sets forth a schematic representation of a Maillard reaction.

DETAILED DESCRIPTION OF THE INVENTION

In the present invention, environmentally friendly or benigncompositions are formed that can, for example, be used to change thepermeability characteristics of subterranean or underground formations(for example, in the recovery of oil and/or other hydrocarbons). Inseveral embodiment of the present invention, when individual polymerchains of the compositions of the present invention interact, chemicalor physical crosslinking may occur. This crosslinking results in athree-dimensional highly branched network of polymers. When thesenetworks become swollen with water (that is, either fresh/deionizedwater of brine) they form hydrophilic gels.

The present inventors have discovered that water soluble polymers havingprimary and/or secondary amine groups form networked gels in thepresence of a reducing saccharide such as a reducing sugar. Reducingsugars are sometimes referred to herein simply as sugars. Similarnetworked or crosslinked polymers gelled in fresh water for use instrengthening paper are discussed in U.S. patent application Ser. No.10/252,262, filed Sep. 23, 2002, the disclosure of which is incorporatedherein by reference. Surprisingly, it has been discovered that networkedgels formed from compositions including polymers having primary and/orsecondary amine groups and a reducing saccharide are quite stable inharsh environments such as experienced in subterranean hydrocarbonrecovery which may include, for example, seawater, brackish water orbrine (that is, water of high salinity or salt content) and temperaturesin excess of 90° C.

Several representative examples of the present invention are describedusing compositions including polymers with vinyl amine repeat groups andat least one of several reducing sugars. Vinyl amine homopolymer wasfound to form relatively stable networked gels in the presence of areducing sugar in both deionized water and water having highsalinity/salt content (simulated seawater). In the studies of thepresent invention in water having high salinity/salt content, simulatedseawater was prepared using procedures similar to those set forth inASTM Standard D 1141-98, Standard Procedure for the Preparation ofSubstitute Ocean Water, the disclosure of which is incorporated hereinby reference. Use of simulated seawater in the gelation studies of thepresent invention was found to have little, if any, effect upon gelationresults as compared to studies carried out with deionized water.

Copolymers of vinyl amine and at least one other monomer were also foundto form networked gels in the presence of a reducing sugar. In manyinstances, use of a copolymer of vinyl amine and at least one othermonomer is preferable to use of a vinyl amine homopolymer in the presentinvention given the expense of the vinyl amine monomer. In a number ofstudies of the present invention, representative copolymers of vinylamine and vinyl alcohol were used. Such copolymers are also sometimesreferred to herein as poly(vinylalcohol)/poly(vinylamine) or PVOH/PVAmcopolymers.

Aqueous solutions (including either fresh/deionized water or simulatedsweater) of poly(vinylalcohol)/poly(vinylamine) copolymer and a numberof sugars were found to gel readily at temperatures between, forexample, approximately 50 and 100° C. In a series of initialexperiments, known amounts of sugars were mixed with a copolymer ofvinyl amine and vinyl alcohol (12 wt % vinyl amine) to form a 40%solution (in water) by weight. The mixtures were heated to varioustemperatures and held for varying lengths of time. Gelation wasdetermined to be the point where a Teflon stir bar ceased to move.

Vinyl amine is required for gelation to occur. In that regard,homopolymers of vinyl alcohol did not gel in the presence of sugar atelevated temperature. Homopolymers of vinyl amine or copolymers of vinylamine and vinyl alcohol gelled readily under these conditions. Reducingsaccharide (for example, sugar) is also required for gelation-vinylamine homopolymers and copolymers of vinyl amine and vinyl alcohol didnot gel without the presence of sugar. Gelation occurs over a wide rangeof amine:sugar (saccharide) ratios.

Gelation occurred in the presence of 2-deoxy-D-ribose, suggesting thatthe osazone mechanism was not responsible for crosslinking. On the otherhand, gelation did not occur when using sucrose, suggesting thatMaillard chemistry (known from food chemistry) is involved in thecrosslinking and hence gelation. Prior studies suggest that nomutagenicity results from products of the Maillard reaction whendisaccharides are employed. Lactose, for example, allows for gelation inthe compositions and systems of the present invention. Although it isbelieved that the Maillard chemistry is involved in gelation in thecompositions of the present invention, the present invention is notlimited to any particular mechanism of gelation.

Increasing temperature increases the rate of the reaction/gelation. Inseveral experiments with a 12% (wt) amine sample, for example, the timefor gelation dropped with increasing temperature from 335 minutes (50°C.) to 113 minutes (60° C.) to 50 minutes (70° C.) to 24 minutes (80°C.) to less than 10 minutes at (90° C.). FIG. 1 illustrates graphicallythe effect of increasing temperature on gel time for a copolymer ofvinyl amine and vinyl alcohol having 6% (wt) vinyl amine. Addition ofacid (for example, H₂SO₄) slowed the gelation reaction, while additionof a base (for example, NaOH) accelerated the gelation reaction (seeFIG. 2).

FIGS. 3 and 4 illustrate studies of the effect of mole ratio of sugar tocopolymer (6% by weight amine) for D-glucose and lactose, respectively.In general, sugar concentration only slightly effected gel time.Moreover, the type of sugar used did not greatly affect gelation time.Lactose was found to be slightly better than D-glucose in these studies.

The gelation of several other hydrophilic polymers and copolymers wasstudied in deionized water and in synthetic seawater. For example,poly(diallyl dimethyl ammonium chloride) [DADMAC] homopolymers werestudied. The PolyDADMAC materials, for example, gelled in deionizedwater and in seawater at 90° C. and 1:1 sugar:PolyDADMAC ratio underbasic conditions. These gels were associative in nature, crosslinkingthough ionic interactions rather than through covalent crosslinkingbonds. The gelation of the polyDADMAC compositions was reversible. Uponaddition of aqueous acid, for example, PolyDADMAC gels rapidly fellapart (dissolved). The PVOH-PVA gels discussed above are, in comparison,permanent in nature (that is, the PVOH/PVA gels comprise covalentcrosslinks).

Compositions of the present invention including copolymers of DADMAC andacrylamide, diallyl amine, and allyl amine (all in 90:10DADMAC/comonomer ratio) were also evaluated in deionized water and insimulated seawater (at 90° C. and 1:1 sugar:copolymer ratio under basicconditions). Each of the compositions appeared to have gelled. Thecompositions gelled more slowly than the PVA-PVOH copolymers discussedabove. Upon gelation, the DADMAC/acrylamide composition became veryviscous or gooey. The DADMAC/acrylamide starting material, however, wasquite viscous, and gelation was thus difficult to determine. TheDADMAC/diallyl amine composition became somewhat more viscous than theDADMAC/acrylamide composition. The DADMAC/allyl amine formed a stiff gel(similar in properties to that formed with the PVOH-PVA copolymers). Themonomer structures and associated polymer repeat units of the DADMAChomopolymer and copolymers are set forth in Table 1. Several of theproperties of the copolymers studied are set forth in Table 2. Theconcentration of DADMAC in the copolymer backbone was maintainedrelatively high to increase the solubility of the copolymers in water.

TABLE 1 Repeat Units of DADMAC and Amine Based Co-Polymers Weight NameUnit Polymer Repeat Unit g/mol Acrylamide

71 Diallylamine

69 Allylamine

57 Diallyldimethyl-aluminumchloride(DADMAC)

161.5

TABLE 2 % of various Bulk % Amine % Viscosity Comonomer DADMAC polymerSolids Cp Acrylamide 90 10 40 13000 Diallylamine 90 10 40 114010-Allylamine 90 10 40 1360

Experimental

Materials. All chemicals were used without further purification.Poly(vinylalcohol) (98-99%, M_(w) 31,000-50,000), D-glucose (A.C.S.reagent) and 2-deoxy-D-ribose (97%) were purchased from Aldrich ChemicalCo. Sucrose (A.C.S. reagent) was purchased from J. T. Baker Chemical.Lactose (A.C.S. reagent) was purchased from E. M. Science. L-ribose(99.5%) was purchased from Acros Organics. Thepoly(vinylalcohol)/poly(vinylamine) copolymers (6 and 12% amine, mediumM_(w)) were donated by Air Products.

Instrumentation. Infrared spectra (IR) were obtained on an ATI MattsonFTIR spectrometer. Information obtained was used to determine chemicalchanges occurring during gelation.

Synthesis of poly(vinylamine). Poly(vinylamine) was synthesized usingN-vinyl formamide (NVF). First poly(vinylformamide) (PNVF) was made bycombining 100 mL of the NVF monomer, 40 mL of DMSO solvent, 61 mg Vazo88 initiator (cyclohexane carbonitrile), and 0.5 g RAFT agent in athree-neck flask. The mixture was then heated at 100° C. for ˜2 hoursunder nitrogen gas with constant stirring and with reflux conditions.After heating, the product was diluted in a 50 mL/50 mL water/ethanolmixture. The product was then precipitated out of solution usingacetone. Product was dried overnight in a vacuum oven, redissolved in a120 mL/50 mL water/ethanol mixture and subsequently precipitated usingacetone. The PNVF was hydrolyzed under basic conditions by combining thepolymer, concentrated NaOH (5% excess) and distilled deionized water ina round bottom flask. The mixture was then heated at 80° C. for 18hours, under reflux conditions and with constant stirring. Adding HCl tothe cold product solution precipitated the product. The product was thenwashed with methanol three times and dried in a vacuum oven. HCl wasremoved by adding aqueous NaOH. This product was precipitated inacetone, dried and then washed with butanol.

EXAMPLES Example 1

An aqueous solution was prepared by dissolving 7.5 g D-glucose and 2.5 gpoly(vinylalcohol) (PVOH) into distilled, deionized water in a 25 mLvolumetric flask. The solution was clear with some undissolved polymer.It was, however, pourable. The solution was transferred to a roundbottom flask and heated to 80° C. in an oil bath. Heating was done withconstant stirring and under reflux conditions. Upon completion thesolution remained clear with all polymer dissolved and was stillpourable.

Example 2

Prior studies suggest that an aqueous solution of PVOH and D-glucosecould be used to form hydrogels by using freezing/thawing cycles. SeeYamaura, K.; Fukada, M.; Tanaka, T.; Tanigami, T. J. of Applied PolymerScience. 1999, 74, 1298-1303. To study this effect, a solution wasprepared as in example 1. Heating was carried out using the sameprocedure as in example 1, but was allowed to reach a temperature of 90°C. The aqueous solution was then placed in a −10° C. freezer over 48hours. After thawing the solution at room temperature for 1 hour a weak,white hydrogel had formed. The gel was then placed back in the freezerfor 24 hours and then thawed at room temperature for 1 hour. Afterwhich, the gel appeared visibly stronger. This gel was found to besoluble in water heated up to 49° C. Neither swelling nor dissolutionwas noted when placed in 1M HCl.

Example 3

Prior studies further suggest that D-glucose was not necessary for thegelation of poly(vinylalcohol) using the process in example 2. SeeYamaura, K.; Karasawa, K. I.; Tanigami, T.; Matsuzawa, S. J. of AppliedPolymer Science. 1994, 51, 2041-2046. To study such gelation, a 2.5 g ofPVOH was dissolved in distilled, deionized water in a 25 mL volumetricflask. Heating was carried out using the same procedure as in example 1,but was allowed to reach a temperature of 95° C. The solution was thenplaced in the freezer at −25° C. for 48 hours. After 1 hour of thawingat room temperature a gel, similar in appearance to the gel in Example2, was produced. The inability of PVOH to form hydrogels without thefreezing/thawing cycle indicated that the amine groups on copolymers ofPVOH and Poly(vinylamine) in the compositions of the present inventionare responsible for gelation.

Example 4

Poly(vinylamine) (PVA) was also used in trying to make gels. An excessof PVA was used in the case that some butanol was still present in thesynthesized polymer. 2.8 g of PVA was dissolved in distilled, deionizedwater in 25 mL volumetric glassware leaving room for the addition ofD-glucose and more water. A heating gun was used, as needed, to dissolvepolymer. D-glucose was dissolved in some water in a separate container,added to the other solution and diluted as necessary. This solution wasorange in color and pourable. Heating was carried out using the sameprocedure as in example 1, but was allowed to reach a temperature of100° C. A rubbery, dark brown gel began to appear at ˜95° C. This gelswelled when exposed to both excess water and 1M HCl.

Example 5

To ensure that the discoloration observed in Example 4 was a result ofgelation and not merely oxidation of the amine, Example 4 was repeatedunder nitrogen gas. This was done using a three neck flask, rubberseptum and needle. The rubbery, dark brown gel appeared at ˜93° C.again. This gel was slightly lighter in color than the gel of Example 5.This gel swelled in water and in 1M HCl.

Example 6

To study whether a sugar was necessary for gelation, 1.25 g of PVA wasdissolved in water in a 25 mL volumetric flask. This solution was thenheated to 95° C. using the procedure of Example 1. No gelation wasobserved.

Example 7

The poly(vinylalcohol)/poly(vinylamine) copolymer that was used for theexperiments set forth in Examples 7 through 24 contained 12% aminegroups. 2.5 g of the copolymer followed by 7.5 g of D-glucose weredissolved in distilled deionized water using the procedure outlined inExample 4. This solution was then transferred to a three-neck flask andheated in an oil bath to 100° C. Heating was carried out under refluxconditions, with constant stirring and under argon gas. A strong, brightyellow gel appeared at ˜90° C. This gel swelled when exposed to excesswater and to 1M HCl.

Example 8

The procedure in example 7 was repeated using 2.5 g D-glucose. This is a1:2 mole ratio of amine groups to sugar molecules. Gelation began tooccur at ˜90° C. This gel was strong and yellow. It swelled in water and1M HCl.

Example 9

The procedure of Example 7 was repeated using 1.25 g D-glucose (a 1:1mole ratio of amine groups to sugar molecules). Gelation began to occurat ˜90° C. This gel was a pale yellow color. This gel is still strongbut not as strong as the previous two examples. Swelling was noted inwater and 1M HCl. IR spectra were taken of the aqueous solution beforeheating and of this gel afterwards. Before heating a strong peak wasseen around 1680 cm⁻¹, which is typical of a primary amine peak. Afterheating this peak became much smaller, more typical of a secondaryamine. Another unidentified peak appeared after heating at ˜1090 cm⁻¹.

Example 10

The procedure of Example 7 was repeated using 0.61 g D-glucose (a 2:1mole ratio of amine groups to sugar molecules). Gelation began to occurat ˜95° C. This gel was strong yet somewhat sticky and a clear yellowcolor. Swelling was noted when exposed to water and to 1M HCl.

Example 11

The procedure of Example 7 was repeated using 0.31 g D-glucose (a 4:1mole ratio of amine groups to sugar molecules). Gelation began to occurat ˜100° C. The gel produced was sticky and almost clear in color. Thisgel swelled when exposed to excess water and to 1M HCl.

Example 12

The procedure of Example 7 was repeated using 0.16 g D-glucose (a 8:1mole ratio of amine groups to sugar molecules). Gelation began to occurat ˜100° C. This gel was sticky and clear. Swelling occurred whenexposed to water and to 1M HCl.

Example 13

To test for the possibility of an osazone mechanism L-ribose was usedinstead of D-glucose. The procedure followed was similar to that ofexample 9 (using a 1:1 mole ratio and the same conditions). 1.02 g ofL-ribose was used. Gelation occurred at ˜85° C. This gel was strong,sticky and bright orange in color. This gel swelled when exposed toexcess water and to 1M HCl.

Example 14

As part of the aforementioned test of reaction mechanism2-deoxy-D-ribose was also used instead of D-glucose. The procedure ofExample 9 was once again followed, this time using 0.91 g of2-deoxy-D-ribose. Gelation occurred at ˜85° C. This gel was also strongand bright orange. The gelation of 2-deoxy-D-ribose indicates that theosazone reaction is not taking place since it would be unable to occuras a result of the structure of this sugar. Without limitation to anyparticular reaction mechanism in the present invention, a Maillardreaction mechanism is thus indicated. The gel of this example swelledwhen exposed to excess water and to 1M HCl.

Example 15

Prior studies show that little or no mutagenicity results from theMaillard reaction when disaccharides, such as lactose, are involved.See, for example, Brands, C. M. J.; Alink, G. M.; vanBoekel, M. A. J.S.; Jongen, W. M. F. J. Agric. Food Chem. 2000, 48, 2271-2275. A summaryof the Maillard reaction is provided in FIG. 6. Thus lactose is a goodsugar for use in the present invention. The procedure of Example 9 wasused, with 2.45 g of lactose. A strong, orange gel formed at ˜100° C.Solubility tests were not carried out on this gel.

Example 16

Sucrose is a disaccharide lacking active carbonyl groups. Therefore,sucrose would not be able to form a gel via the Maillard reaction. SeeBaynes, J. W.; Monnier, V. M. “The Maillard Reaction in Aging, Diabetesand Nutrition” 1989; and O'Brien, J.; Nursten, H. E.; Crabbe, M. J. C.;Ames, J. M. “The Maillard Reaction in Foods and Medicine” 1998. Theprocedure from example 9 was once again repeated. In this example, time2.33 g of sucrose was used. The temperature was taken up to 115° C. andgelation was not observed.

Example 17

Constant temperature experiments were also carried out. 2.5 g ofcopolymer followed by 1.25 g of D-glucose were dissolved in water usinga 25 mL volumetric flask as outlined in Example 4. Heating took place inan oil bath that was maintained at a constant temperature of 80° C.Heating was done under reflux conditions, under argon gas and withconstant stirring. Gelation time was noted as the time when the gelbecame too viscous for the stir bar to move. In this example gelationtime was found to be 23.5 minutes. The gel produced was a clear yellowand sticky. This gel dissolved in water.

Example 18

The procedure of Example 17 was repeated using an oil bath at 70° C.Gelation time was noted as 49.5 minutes. This gel was weaker andstickier than the previous one. This gel also dissolved in water.

Example 19

The procedure of Example 17 was repeated using an oil bath at 60° C.Gelation time was noted as 113.25 minutes. This gel was weaker andstickier than the previous one. This gel also dissolved in water.

Example 20

The procedure of Example 17 was repeated using an oil bath at 50° C.Gelation time was noted as 335.0 minutes. This gel was weaker andstickier than the previous one. This gel also dissolved in water.

Example 21

To test the effect of pH on gelation, the procedure of Example 17 wasrepeated under acidic conditions. Three drops of concentrated H₂SO₄ wereadded to the aqueous solution. After 120.0 minutes the solution hadturned slightly yellow and appeared to be a pourable gel. This gel wasalso soluble in water.

Example 22

Basic conditions were also examined using the procedure in example 17.0.04 g of concentrated NaOH were added to the aqueous solution. Gelationwas noted after 18.2 minutes. This gel was similar in appearance to thatproduced in Example 17. This gel was slightly soluble in excess water.

Example 23

The gels studied in FIGS. 1 through 5 were synthesized in a consistentmanner. In that regard, 21.25 grams of copolymer was weighed out into abeaker and set aside for both 6 wt % and 12 wt % amine copolymers. Thesugar was also weighed out in a beaker and set aside. The amount ofsugar added depended on the mole ratio of sugar to amine, which isindicated in Table 3 below for each ratio.

TABLE 3 Molar Ratio (sugar:amine) And Type of Sugar Amount of Sugar(grams) 1:1 glucose 5.23 2:1 glucose 10.46 4:1 glucose 20.92 1:2 lactose5.23 1:1 lactose 10.46 2:1 lactose 20.92The saccharide (sugar):amine rations set forth in Table 3 and FIGS. 3and 4 are merely the reciprocal of amine:sugar mole ratios.

Water (deionized water or simulated seawater) was measured out in a tallform beaker to approximately 425 mL. A small amount (˜¼) of this waterwas put into another tall form beaker and the sugar was added and mixedthoroughly. The bulk of the water was used to mix with the copolymer.The mixture of copolymer/water was then put into an oil bath and mixedto allow the copolymer to dissolve. Next, the sugar/water mixture wasadded into the copolymer mixture and the time was started. The ULadapter was then lowered into the mixture and the Brookfield viscometerwas turned on to a speed of 60 (The Brookfield viscometer had beenearlier calibrated with water). The readings form the Brookfield werenot recorded until after the time had reached 9 minutes to allow the ULadapter to settle. The time was then recorded after each minute. Theonly other change in procedure occurred when the NaOH was added [50%(w/w/) NaOH in water solution]. 31 mM of NaOH (or 1 gram of the NaOH inwater solution) was added into the sugar/water mixture before adding itto the copolymer mixture.

Example 24

Synthetic or simulated seawater was prepared with reference to ASTMStandard D 1141-98 Standard Practice of the Preparation of SubstituteOcean Water. Unlike the solution prepared in the ASTM standard, thesynthetic seawater used in the studies of the present invention was notprepared by mixing of separate stock solutions, but by direct mixing ofthe items listed in Table 4 to achieve the approximate concentrationsset forth in Table 4. The minor component compounds H₃BO₃, SrCl₂ and NaFof the ASTM standard (having concentrations of 0.027 g/L, 0.025 g/L and0.003 g/L in the ASTM standard) were not added.

ASTM Standard D 1141-98 (2003) indicates the chlorinity of the resultantsynthetic ocean or seawater to be 19.38 ppt, which is approximatelyequivalent to a salinity of 35.01 ppt (using the equation S=1.80655 Cl).

TABLE 4 Compound Concentration (g/L) NaCl ~24.5 MgCl₂ ~5.2 Na₂SO₄ ~4.1CaCl₂ ~1.2 KCl ~0.7 NaHCO₃ ~0.2 KBr ~0.1 H₃BO₃ 0 SrCl₂ 0 NaF 0

Example 25

In a representative example of synthetic procedure of a poly(diallyldimethyl ammonium chloride) (DADMAC)/allyl amine copolymer of thepresent studies, the reaction was carried out in a 1 L, four-neckedresin pot equipped with a mechanical stirrer, a thermometer, acondenser, a purge tube and a heat regulator. Approximately 492 g of a55% aqueous monomer solution including 75 wt % DADMAC and 25 wt % allylamine was added to the reaction vessel and stirring commenced. The pHwas then adjusted to approximately 6.0 by addition of dilute HCl. Theresultant reaction mixture was heated to 50° C. and purged with nitrogenfor 1 hour. Subsequently 500 ppm of sodium EDTA (based upon the weightof the reaction mixture) was added, followed by addition of 1.5×10⁻²mole t-butyl peroxypivalate per mole of monomer. The temperature of thereaction mixture was maintained at 50° C. for 10 hours.

Example 26

Poly(diallyl dimethyl ammonium chloride) (DADMAC) homopolymers at 5 wt %were gelled in seawater at 90° C. and 1:1 sugar:DADMAC under basicconditions. Gelation was observed. Upon addition of aqueous acid thegels rapidly fell apart (dissolved), indicating that the gels wereassociative in nature.

Example 27

Several experiments were performed to observe the crosslinking reactionof diallyl dimethyl ammonium chloride/acrylamide copolymer, diallyldimethyl ammonium chloride/diallyl amine copolymer, and diallyl dimethylammonium chloride/allyl amine copolymer at 5 wt % in seawater at 90° C.and at a 1:1 sugar:copolymer ratio. The allyl amine co-polymer, forexample, resulted in a relatively stiff polymer network. Addition ofwater to the polymer network resulted in gelation/expansion to well over500% the original volume. The resultant gel was a very viscousmonolithic type gel. The polymer was subsequently heated to remove theseawater, followed by addition of more seawater to determine if theprocess of expansion was repeatable. These studies indicated that thegel was able to be “expanded” and “compressed” multiple times.

The foregoing description and accompanying drawings set forth preferredembodiments of the invention at the present time. Various modifications,additions and alternative designs will, of course, become apparent tothose skilled in the art in light of the foregoing teachings withoutdeparting from the scope of the invention. The scope of the invention isindicated by the following claims rather than by the foregoingdescription. All changes and variations that fall within the meaning andrange of equivalency of the claims are to be embraced within theirscope.

1. A composition comprising: water having a salinity of at least 1 ppt;at least one hydrophilic polymer containing at least two groups whichare independently the same or different a primary amine group or asecondary amine group and at least one saccharide containing a reduciblefunction.
 2. The composition of claim 1 wherein the water has a salinityof at least 3 ppt.
 3. The composition of claim 1 wherein the water has asalinity of at least 10 ppt.
 4. The composition of claim 1 wherein thewater has a salinity of at least 10 ppt.
 5. The composition of claim 1wherein the water has a salinity of at least 35 ppt.
 6. The compositionof claim 1 wherein the reducing saccharide is a monosaccharide, adisaccharide or a polysaccharide.
 7. The composition of claim 1 whereinthe polymer is partially hydrolyzed poly(N-vinylformamide), partiallyhydrolyzed vinyl acetate/N-vinylformamide copolymer, hydrolyzedacrylonitrile/N-vinylformamide copolymer, amine functionalpolyacrylamide, acrylic acid/vinylamine copolymer, maleicanhydride/maleic acid copolymers with N-vinylformamide/vinylamine,N-vinylformamide/vinylamine polymers with vinyl sulfonate comonomerunits, allylamine polymer, diallylamine polymer, allylamine/diallylaminecopolymer, urea/formaldehyde condensation polymers,melamine/formaldehyde condensation polymers, amidoamine polymers,amine/epichlorohydrin polymers, poly(ethyleneimine), hydrolyzedpoly(2-alkyl-2-oxazoline), partially hydrolyzedpoly(2-alkyl-2-oxazoline), poly(diallyl dimethyl ammonium chloride),diallyl dimethyl ammonium chloride/acrylamide copolymer, diallyldimethyl ammonium chloride/diallyl amine copolymer, or diallyl dimethylammonium chloride/allyl amine copolymer.
 8. The composition of claim 1wherein the polymer is a copolymer of vinyl amine and vinyl alcohol. 9.The composition of claim 8 wherein the copolymer is at least 0.5% byweight of vinyl amine.
 10. The composition of claim 8 wherein thecopolymer is at least 3% by weight of vinyl amine.
 11. The compositionof claim 8 wherein the copolymer is at least 6% by weight of vinylamine.
 12. The composition of claim 8 wherein the copolymer is at least12% by weight of vinyl amine.
 13. The composition of claim 1 wherein themole ratio of amine to reducing saccharide is in the range ofapproximately 1:4 to approximately 8:1.
 14. The composition of claim 1further comprising a base.
 15. The composition of claim 14 wherein thebase is sodium hydroxide, potassium hydroxide, ammonia or calciumcarbonate.
 16. The composition of claim 1 wherein the saccharide is atleast one of glucose, lactose, or 2-deoxy-D-ribose
 17. The compositionof claim 1 wherein the hydrophilic polymer is poly(diallyl dimethylammonium chloride), diallyl dimethyl ammonium chloride/acrylamidecopolymer, diallyl dimethyl ammonium chloride/diallyl amine copolymer ordiallyl dimethyl ammonium chloride/allyl amine copolymer.
 18. Thecomposition of claim 17 wherein the hydrophilic polymer is diallyldimethyl ammonium chloride/acrylamide copolymer, diallyl dimethylammonium chloride/diallyl amine copolymer or diallyl dimethyl ammoniumchloride/allyl amine copolymer.
 19. The composition of claim 18 whereinthe content of diallyl dimethyl ammonium chloride in the copolymer is atleast 50 weight percent.
 20. The composition of claim 18 wherein thecontent of diallyl dimethyl ammonium chloride in the copolymer is atleast 70 weight percent.
 21. The composition of claim 18 wherein thecontent of diallyl dimethyl ammonium chloride in the copolymer is atleast 80 weight percent.
 22. The composition of claim 17 wherein thehydrophilic polymer is diallyl dimethyl ammonium chloride/diallyl aminecopolymer or diallyl dimethyl ammonium chloride/allyl amine copolymer.23. The composition of claim 1 wherein the composition form a covalentlycrosslinked polymer network.
 24. The composition of claim 1 wherein thecomposition forms an ionically crosslinked polymer network. 25-51.(canceled)